1. Field of the Invention
This invention relates generally to coated articles, e.g., coated automotive transparencies, and to methods of changing the visible light transmittance of the coated articles.
2. Description of the Currently Available Technology
It is known to reduce the heat build-up in the interior of a vehicle by providing a laminated windshield having two glass plies with an infrared (IR) or ultraviolet (UV) attenuating solar control coating positioned between the plies. The plies protect the solar control coating from mechanical and/or chemical damage. These conventional windshields are generally made by shaping and annealing two flat glass “blanks” (one of which has the solar control coating deposited thereon) to form two shaped, annealed glass plies and then securing the glass plies together with a plastic interlayer. Because conventional solar control coatings include metal layers that reflect heat, the glass blanks are typically heated and shaped as “doublets”, i.e., the blanks are positioned one on top of another during heating and shaping with the functional coating sandwiched between the glass blanks to prevent uneven heating and cooling, which can affect the final shape of the plies. Examples of laminated automotive windshields and methods of making the same are disclosed in U.S. Pat. Nos. 4,820,902; 5,028,759; and 5,653,903.
The heatability of the doublet is generally limited by the ability of the functional coating to withstand the heat treatment without adversely degrading. By “heatability” is meant the maximum temperature and/or maximum time at a particular temperature to which the coated substrate can be heated without degradation of the functional coating. Such degradation can affect the physical and/or optical properties of the coating, such as solar energy reflection and/or transmission. Such degradation can be caused, for example, by oxidation of various metal-containing layers in the functional coating. For example, functional coatings containing metal layers can be sensitive to oxygen in that there can be some change, e.g., decrease, in the optical and/or solar control properties of the functional coating when the coated substrate is heat treated, such as by heating, bending, annealing, or tempering, for use in a motor vehicle transparency or window or vision panel, or for use in residential or commercial windows, panels, doors, or appliances.
It would also be advantageous to provide a solar control coating on other automotive transparencies, such as sidelights, back lights, sunroofs, moon roofs, etc. However, the processes of making laminated windshields are not easily adapted to making other types of laminated and/or non-laminated automotive transparencies. For example, conventional automotive sidelights are usually made from a single glass blank that is individually heated, shaped, and tempered to a desired curvature dictated by the dimensions of the vehicle opening into which the sidelight is to be installed. A problem posed in making sidelights not encountered when making windshields is the problem of individually heating glass blanks having a heat-reflecting solar control coating.
Additionally, if the sidelight is positioned such that the coating is on the surface of the sidelight facing away from the vehicle (the outer surface), the coating is susceptible to mechanical damage from objects hitting the coating and to chemical damage from acid rain or car wash detergents. If the coating is on the surface of the sidelight facing the interior of the vehicle (the inner surface), the coating is susceptible to mechanical damage from being touched by the vehicle occupants or from being rolled up and down in the window channel, and to chemical damage from contact with conventional glass cleaners. Additionally, if the coating is a low emissivity coating it can promote a greenhouse effect trapping heat inside the vehicle.
While it is known to reduce chemical damage or corrosion to a coating by overcoating with a chemically resistant material, these overcoats are typically applied as thin as possible so as not to adversely affect the optical characteristics (e.g., color, reflectance, and transmittance) of the underlying coating and so as not to significantly increase the emissivity of the underlying coating. Such thin overcoats typically do not meet the durability requirements for shipping, processing, or end use of conventional coated automotive transparencies, which are easily damaged and continuously exposed to the environment. Additionally, such thin overcoats would not alleviate the greenhouse effect problem discussed above. Examples of conventional overcoats are disclosed in U.S. Pat. Nos. 4,716,086; 4,786,563; 5,425,861; 5,344,718; 5,376,455; 5,584,902; and 5,532,180.
Therefore, it would be advantageous to provide a method of making an article, e.g., a laminated or non-laminated automotive transparency, or panel, or sheet having a functional coating that reduces or eliminates at least some of the problems discussed above.
Additionally, some areas of an automobile, such as rear sidelights, moon roofs, sunroofs, and the like, typically utilize so-called privacy glass. By “privacy glass” is meant glass having a lower visible light transmission than the windshield and/or front sidelights. Typically, privacy glass has a visible light transmittance of less than 50% and appears dark or black in color. Conventional privacy glass can be formed by adding colorants to the glass batch materials to color or shade the resultant glass article. While decreasing visible light transmittance, conventional privacy glass typically does not provide significant solar radiation reflective properties. Therefore, it would also be advantageous to provide a method of making a coated article, e.g., useful as a privacy glass. It would further be advantageous to provide a method of providing an article of a desired color or shade. It would also be advantageous to provide a method of preventing color and/or chemical changes to coatings upon heating.